Patent GB-1296405-A (GB)
IPC: G08C15/12
Filed: 1970-02-17
Abstract: 1296405 Selective signalling INSTRUMENT SYSTEMS CORP 17 Feb 1970 [20 Feb 1969 (2) 5 Sept 1969] 7576/70 Heading G4H [Also in Division H4] In an entertainment service system, e.g. for an aircraft, a number of programmes are broadcast in time division multiplex on a single line feeding a number of stations, e.g. one at each seat. Each station has a selector and a transducer, whereby a selected programme can be reproduced on the transducer at that station. Each station also has utilization control means each associated with respective utilization circuits, e.g. for service call lights or lamps for general illumination or reading. The local utilization controls are connected to local coders which are connected in series with a central timer. Local decoders associated with the respective utilization circuits are also connected in series with the central timer. The coders and decoders are activated sequentially by the timer to allow the local control to effect operation of the respective utilization circuit. As described, a main multiplexer 12, Fig. 1, is fed with a 10-channel audio input and pulse code modulated samples of the signals in each channel are time division multiplexed on to a single line 13 for distribution to a number of submultiplexers 14 where respective groups of 5 audio channels are added to the signals from the main multiplexer. The additional signals may be in respect of films or other entertainment particular to a respective zone of the aircraft. Each zone submultiplexer 14 feeds a number of local demultiplexers 18 feeding a group of transducers 20, e.g. located in a row of seats, each of which has a local control 22 to enable selection of the programme to be reproduced. Audio channel samples may be prefixed by a "stereo-tag" signifying that a pair of channels are to be reproduced by the transducers when that channel is selected. An override public ,address arrangement is provided to enable announcements to be reproduced at each transducer irrespective of the channel selected at the respective selector. Each local control is also connected to a local coder 28, all of which are located in a loop between lines 32 and 34 connected to the column timer 26. The coders are arranged to receive clock pulses from the column timer over the loop and respond sequentially so that signals indicating the states of the local utilization controls are fed back sequentially to the column timer from which they may be transmitted, together with clock signals, to the local decoders 30, to be selected and applied sequentially to the respective utilization circuits 24. In one system, as shown in Fig. 1, the data from the coders is transmitted over a common line 32, this system is the subject of divisional Specification 1,296,408, in an alternative arrangement the data is transmitted back through the previously operated coders, to reach the appropriate decoder via the previously operated decoders, this system is the subject of divisional Specification 1,296,407. A testing arrangement is provided which applies a test signal of predetermined frequency to the inputs of the audio channels. When received at the local control stations they cause overriding of the service call lamp control to produce an effect equivalent to the repetitive opening and closing of the control switch. The effect is arranged only to occur if the transducers associated with the control station are effective and to be inhibited if the transducers are open circuit. The testing system is the subject-matter of divisional Specification 1,296,406.